As the technologies for controlling the floor reaction force acting on the distal portions of the legs of a legged mobile robot, such as a bipedal mobile robot, when making the robot travel by causing the distal portions of its legs to come in contact with or leave a floor, there have been known the technologies disclosed in Japanese Unexamined Patent Application Publication No. H5-305585 (Patent Document 1), Japanese Unexamined Patent Application Publication No. H10-277969 (Patent Document 2) and Japanese Unexamined Patent Application Publication No. 2001-322076 (Patent Document 3) by the present applicant.
However, these technologies are originally based on an assumption that the distal portions of the legs are brought into contact with a floor to make the robot travel, and therefore, sensors for detecting floor reaction forces are provided in the distal portions of the legs. Further, there has been also known a technology in which power sensors are provided in the distal end portions of arms to control forces acting on the distal portions of the arms when making a robot having arms perform a certain job.
In these conventional robots, it is basically assumed that external forces, such as floor reaction forces, act on the distal portions of their legs or arms, and places, such as knees, other than the distal portions of the legs or arms are not provided with sensors for detecting external forces. Hence, it has been impossible to control external forces (e.g., floor reaction forces) acting on the knees.
For example, in a state wherein a conventional human-like robot is kneeling, the floor reaction force acting on the right and left knees are dependent upon (governed by) the projections and depressions of a floor, and no adjustment of the joint angles of the legs has been made on the basis of the projections and depressions of the floor. For this reason, there have been cases where a projection or a depression causes a portion of the robot that comes into contact with a floor shakes, resulting in unstable contact condition of the portion coming into contact. Under this condition, an attempt to make the robot operate or work has sometimes led to an unstable posture of the robot.
Furthermore, when, for example, a robot stands up from a kneeling posture, if the actual inclination of a floor is different from the inclination assumed in a desired gait, then there has been a danger in that the robot falls, because the position of the center-of-gravity of the robot is not properly controlled and the robot undesirably tries to stand up with its body posture inclined.
Moreover, in a case where a robot operates or works while sitting in a chair, maintaining its stable postures, it is desired that the reaction forces applied from the chair to the buttocks of the robot as well as the floor reaction forces acting on the feet of the legs of the robot can be properly controlled in order to make it possible to restore the posture of the robot to a proper posture when the robot rises from the chair or sits onto the chair.
The present invention has been made with a view of the background described above, and it is an object thereof to provide a control system for a mobile robot that properly controls not only external forces acting on the distal portions of legs and arms of the robot but also external forces acting on portions other than the distal portions of the legs and arms in a state wherein the portions of a mobile robot, such as knees, elbows, the trunk, and buttocks, other than the legs and arms are subjected to external forces when they come in contact with a floor or an object considered as an extension of the floor, thus making it possible to maintain stable postures of the mobile robot.